The present invention relates to retractable cover or tarping systems, and especially retractable tarping systems for use on a flat bed trailer.
Flat bed trailers are used to haul a variety of goods ranging from large heavy articles such as machinery to palletized goods. It is desirable, particularly with regard to weather sensitive goods, to provide a cover to protect a load during transit. Various types of cover systems have been used ranging from simple tarps held in place with cargo straps and tie downs to retractable tarp systems that cover and protect the entire trailer bed from weather and debris.
One such retractable tarp system is the CONESTOGA® tarp cover system manufactured and sold by Aero Industries of Indianapolis, Ind. Certain details of this type of cover system are disclosed in the U.S. Pat. No. 4,711,484, issued on Dec. 8, 1987, U.S. Pat. No. 4,902,064, issued on Feb. 20, 1990, and U.S. Pat. No. 5,538,313, issued on Jul. 23, 1996, all of which are owned by the assignee of the present invention. The disclosures of the '484, '064 and '313 Patents are incorporated herein by reference. The CONESTOGA® tarp system was developed to provide a tarp cover system that not only effectively encloses the cargo area but also protects or seals the tarp cover deployment system. The CONESTOGA® system includes a wheel and track deployment system that is supported at the outside edges of the trailer. In this manner, the entire trailer bed and the cargo are under cover.
A typical CONESTOGA® system installation is depicted in FIG. 1. In particular, the retractable tarping system 10 is mounted on the trailer flat bed T. The system 10 includes a flexible cover or tarpaulin 12 that can be folded or pleated as the rear and front bulkheads 13, 14 are drawn together. The tarp 12 is supported between the bulkheads by a bow structure 15. The bow structure includes a plurality of intermediate U-shaped bows 16 that span the width of the flat bed T. Each end of the bows is mounted to a carriage 18 that is slidably supported on corresponding rail 20 fixed to the flat bed. The carriages are configured so that they move along the rails to extend or retract the tarp system 10.
With flexible cover systems like the CONESTOGA® system, it is important to keep the tarp cover in tension. The tensioned tarp more effectively seals the cargo area from the elements, and resists flapping due to wind and road vibration. In the typical extendable tarp system, the tarp cover is stretched slightly on deployment and latched to rear and front bulkheads 13, 14. The CONESTOGA® system incorporates tensioning and locking mechanisms at the opposite ends of the tarp 12 to maintain this tension. The CONESTOGA® system includes tensioning mechanisms that account for changes in the length of the tarp over time. It is known that the tarp 12 will stretch as it is maintained in tension in its extended position. Thus, the tensioning mechanisms are configured to maintain longitudinal tension in the tarp that is uniform over the useful life of the tarping system.
In addition, the bow structure 15 incorporates bow elements that extend slightly above the plane of the top of the intermediate bows 16. For instance, the CONESTOGA® system includes U-shaped primary uplift bows 24 that are situated between successive intermediate bows 16. The uplift bows 24 are supported on the carriages 18 by legs 25. The primary uplift bows 24 are configured so that as the carriages 18 are retracted or moved towards each other, the bows 24 are elevated as the legs 25 are moved to a more vertical orientation. Thus, the primary uplift bows 24 help pleat or fold the tarp 12 as the tarp system is retracted, providing for a uniform retraction and avoiding problems with bunching of the tarp between intermediate bows 16.
Additional support for the tarp 12 may be provided by secondary uplift bows 30, sometimes called a triple uplift bow because two such bows 30 flank the intermediate bow 16. The U-shaped secondary uplift bows 30 are pivotably mounted to the intermediate bow 16 at a pair of brackets 32 fastened to opposite sides of the intermediate bow, as shown in FIGS. 2-3. Typically, the uplift bows 30 are tubular so they include a hollow interior 31. A cotter pin 34 passes through openings 38 in the arms of the bracket 32, and through bushings 36 pressed into openings 40 in the tubular bows 30. A washer 42 and cotter pin retainer 44 fix the cotter pin 34 to the bracket 32, which in turn pivotably mounts the end of the secondary uplift bow 30 to the intermediate bow 16. As with the primary uplift bows 24, the secondary bows 30 lift the tarp 12 to maintain the top of the tarp in tension. In addition, as the tarp system is retracted, the secondary uplift bows 30 pivot to a more vertical orientation, which again helps pleat or fold the tarp 12 as it is retracted and compressed.
In a typically cover or tarping system, the horizontal portions of the bows 16, 24 and 30 are held in contact with the tarp 12. Thus, in some systems, the tarp includes pocket spaced along the top of the tarp through which the horizontal portions of the bows extend. In other systems, a series of straps along the top of the tarp are used to connect the bows to the tarp. These straps may include a self-engaging fastener, such as VELCRO® ends, to make the connection.
It was noted above with respect to the tensioning and locking mechanisms that tarp 12 tends to stretch over time as it is repeatedly tensioned and relaxed. The tensioning mechanisms are useful to longitudinally tension the tarp, especially at the lower portions of the tarp. The bow system 15 is configured to help maintain the upper portion of the tarp in tension. However, even as the lower part of the tarp stretches, so too will the top of the tarp. In current tarping systems, the bow structures are not automatically capable of accounting for changes in length, and ultimately tension, in the top of the tarp. As the top of the tarp stretches, it begins to flap against the fixed dimension uplift and intermediate bows. What is needed, therefore, is a bow structure that automatically adjusts to the changing characteristics of the tarp that the bow structure is supporting.